The present invention relates generally to bearings and, more particularly, to a dual-mode twin-chamber bearing having hydraulic damping.
A dual-mode twin-chamber bearing having hydraulic damping is particularly suited for use as an engine bearing in an engine in a motor vehicle. The bearing has a working chamber and an equalizing chamber separated by a partition. A damping channel or optionally additional vibration damping devices, hydraulically connects the chambers. The partition has a passage at its center. An actuator can close the passage, and the outer wall of the equalizing chamber is formed by bellows.
A dual-mode bearing of the type discussed here is known, for example, from U.S. Pat. No. 5,344,127, which is incorporated by reference. Reference is made to the operation of such a bearing described in that document. Bearings of this type have been successfully used for damping both low-frequency and high-frequency vibrations. When the passage in the partition is closed, high-frequency low-amplitude vibrations are damped by the design of the partition and the membrane arranged therein. As soon as the passage in the partition is opened, low-frequency vibrations are damped. The passage in the partition is closed by a piston, which is actuated by a control pressure box. The control pressure box is pneumatically actuated, vacuum being preferably applied to it when the passage is to be closed.
Developments are being pursued in the automobile industry which render vacuum pumps unnecessary. The dual-mode thrust bearing can thus no longer be equipped with vacuum chambers. Therefore, methods operating the dual-mode thrust bearing without the use of a vacuum chamber are being sought. The design of the mechanism must be simple, compact, and sturdy.
The above problem is solved by providing a dual mode thrust bearing which is actuated by an electric motor. The thrust bearing has a working chamber and an equalizing chamber. A partition separates the two chambers, and the partition has a passage closable by an actuator. A damping channel also hydraulically connects the two chambers. The outer walls of the equalizing chamber are formed by elastic bellows, and the actuator and the bellows are an integral component. An electric motor displaces the actuator via an actuator mechanism to close the passage.
The use of an electric motor is particularly advantageous, since pneumatic lines to a control pressure box, as well as the control pressure box itself, are not needed. The actuator mechanism has a simple design in that it is a cam disk connected to the shaft end of the electric motor. The actuator is pressed onto the cam disk by the slightly pressurized fluid in the equalizing chamber via the actuator plunger. This ensures that the plunger rests on the cam disk in any operating position. In order to reduce friction between the plunger and the cam disk, a ball may be arranged at their contact surfaces.
The elastic bellows forming the equalizing chamber is preferably designed as a roller bellows. The actuator is inserted in the center of this roller bellows. This can be accomplished by making the actuator a separate part which is welded to the roller bellows. It is, however, also possible to provide the roller bellows with a closing piston directed inward and a plunger directed outward connected thereto. The roller bellows can also be designed so that it has an initial stress directed outward and it attempts to press the plunger outward due to this pre-stress alone. The pre-stress will therefore cause the plunger to be pressed against the cam disk.
According to a further aspect of the invention, a gear is located between the electric motor and the cam disk. This allows a higher-speed electric motor to be used.
In order to guarantee the stability of the arrangement, it is advantageous to arrange at least part of the electric motor in a housing which can in turn be placed in the bearing cover mounted on the thrust bearing. This allows the use of the smallest possible motors.
In another embodiment of the present invention, the end of the electric motor protruding from the housing and/or the gear cladding is framed by a friction bearing, on which the cam disk is rotatably mounted. The friction bearing is in turn attached to the housing. Thus the forces from the actuator are transmitted to the housing without any bending moments. In addition, the load on the shaft end of the gear is relieved, which produces very cost-effective results.
In order to attach the cam disk to the gear shaft, the cam disk is provided with a hub-like part, which is attached to the gear shaft. The cam disk and the hub-like part form a single unit.
In order to prevent the cam disk from twisting when the motor is not in operation, it may be provided with notches, which engage correspondingly designed fillets of the plunger.
The entire assembly made up by the bearing cover, electric motor housing, electric motor, gear and the cam disk mounted on it is manufactured as a module and connected to the hydraulic part of the hydraulic bearing. As a further development of this idea, modules that can be attached to existing hydraulic bearings can also be manufactured, so that, for example, the above-described actuating mechanism having the control pressure box can be replaced by this module.